Reactions, coupled light, primary

Primary active transporters Group of transporters that couple the energy of a chemical reaction or light on one side of the membrane to the transport of a solute. 

Of some importance as textile dyes are aza analogues of polymethine (cyanine) dyes. Azacarbocyanines result when Fischer s aldehyde is heated with primary aromatic amines. Thus Cl Basic Yellow 11 (6.220) is obtained when Fischer s aldehyde is condensed with 2,4-dimethoxyaniline. The equivalent reaction with 2-methylindoline gives Cl Basic Yellow 21 (6.221), which has superior light fastness but has been classified by ETAD as toxic [73]. The tinctorially strong golden yellow diazacarbocyanine dye Cl Basic Yellow 28 (6.222) is prepared by coupling diazotised p-anisidine with Fischer s base (6.223), followed by quaternisation with dimethyl sulphate. Some triazacarbocyanine dyes are also used commercially. 

Several, oxidatively coupled xanthates (64-66), compounds (also called xanthides) containing the photochemically reactive, sulfur-sulfur bond, have been studied.130 Homolytic cleavage of this reactive bond is the primary reaction for these compounds, although this process is normally masked by recombination of the radicals produced. This primary, light-initiated process becomes apparent when a mixture of the xanthide 64 and ethyl xanthide (67) is irradiated in cyclohexane, because an equilibrium between 64, 67, and the mixed xanthide 68 is rapidly established. 

In an early review2 A. J. Hoff called the primary processes of photosynthesis a Garden of Eden for EPR spectroscopists . And indeed this techniques plays until today a major role in this field of research and the results derived from EPR and related experiments have contributed very substantially to our knowledge about the details of the light-induced processes and of the coupled enzymatic reactions. 

It should be said, however, that the initial light signal associated with the photoisomerization of the photochromic moiety is usually a weak effect, and requires amplification in order to construct photoswitchable devices. The greater the amplification factor, the greater is the sensitivity of the system. Substantial amplification can be achieved when the primary photochemical reaction is coupled with a subsequent event that occurs after absorption of light. 

The term ion pump, synonymous with active ion-transport system, is used to refer to a protein that translocates ions across a membrane, uphill against an electrochemical potential gradient. The primary pumps do so by utilization of energy derived from various types of chemical reactions such as ATP hydrolysis, electron transfers (redox processes), and decarboxylations, or from the absorption of light (Table 1). Secondary pumps are symport and antiport systems that derive the energy for uphill movement of one species from a coupled downhill movement of another species. The electrochemical gradient driving the latter movement is often created by a primary pump. 

An essential feature of reactions catalyzed by metal-sulfur oxidoreductases is the coupling of proton- and electron-transfer processes. In this context, an important question is how primary protonation of metal-sulfur sites influences the metal-sulfur cores, small molecules bound to them, and the subsequent transfer of electrons. In order to shed light upon this question, protonations, isoelectronic alkylations, and redox reactions of [M(L) (S )] complexes were investigated (M = Fe, Ru, Mo L = CO, NO S = Sj, US24 ). The CO and NO ligands served as infrared (IR) probe for the electron density at the metal centers. Resulting complexes were characterized as far as possible by X-ray crystallography. Scheme 23 shows examples of such complexes. 

Chemiluminescent labels may be employed in sandwich or competitive antigen assays. In sandwich assays, a solid support holds a primary antibody, and incubation with ligand yields a species that is detectable following a second incubation step with a labeled second antibody. Luminol has been tested as an immunoassay label it may be coupled to proteins through its primary amino group. Luminol reacts with hydrogen peroxide and hydroxide in a microperoxidase-catalyzed reaction, which yields light at 430 nm (Eq. 6.8) ... 

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